The invention generally relates to roll cleaning apparatus for web or sheet production processes, and relates in particular, to roll cleaning apparatus for rolls in papermaking machines and web converting machines.
In a papermaking machine, web converting operation, or any other web or sheet production process it is often necessary to clean and/or condition the rotating roll surfaces or other moving surfaces that are used to convey the product. Inadequate cleaning of these moving surfaces will result in a build-up of contaminants and debris that may lead to product defects and production losses.
The contaminants that build up on these moving surfaces may include adhesive residue from use of recycled fiber, pitch, precipitated calcium carbonate (PCC), clay, starch or other polymers from coatings used in the product. Prior art cleaning systems generally utilized to remove contaminants on these moving surfaces include doctoring systems as well as abrasive pad type cleaning systems.
The doctor systems used for cleaning a roll generally employ a doctor blade to scrape the moving surface of a roll. Such doctor blades are generally effective in removing water, fiber build up and the product itself during threading or when a sheet break occurs. Doctor blades are also generally effective at removing contaminants of some appreciable thickness which allows the working edge of the blade can get underneath and lift the contaminant away from the moving surface. Such doctor blades however, are not typically very effective at removing contaminants (or haze) that is of a very small particle size and may be in the microscopic grooves or pores of the roll surface. Additionally, doctor blades are not typically very effective at removing contaminants of minimal thickness (<0.010 inches) and that are adhered to the moving surface with a very high bond strength.
Other prior art cleaning systems include a device that applies an abrasive pad against a moving surface such as a roll surface. United States Published Patent Application Publication No. 2005/0177971, for example, discloses an apparatus for cleaning a roll in a papermaking machine, wherein a cleaning pad that conforms to the surface of a roll is mounted on a movable support structure that is movable into engagement with the roll surface. FIG. 1, for example, shows an embodiment that includes a scrubbing element 10 attached to a backing member 12, which in turn is attached to brackets 14 via fasteners 16. A longitudinal motion drive 18 is employed to move the brackets 14 via bearings 20 mounted on a block 22 in a reciprocal scrubbing motion. The drive 18 and block 22 are mounted on a movable plate 24 that is moveable with respect to a base plate 26 about a pin 28 via actuation of pneumatic bellows 30 such that the scrubbing element 10 is moved through a gap G into and out of engagement with a surface of a roll 32. The position of the base plate 26 is bounded by a standoff 34 and a stop 36.
FIG. 2 shows another embodiment of a prior art cleaning pad and backing member also disclosed in United States Published Patent Application Publication No. 2005/0177971 that provides vacuum pressure near the roll surface. In particular, FIG. 2 shows a cleaning head assembly that has a backing member 40, which provides an internal plenum 42, and a roll engagement wall 44 to which an abrasive pad 46 is attached via fasteners 48 and 50. The wall 44 is disclosed to include grooves 52, 54, 56, 58, 60, 62 as well as apertures therein through which dust and lint particles are disclosed to be drawn by vacuum into the plenum 42 and exhausted from the cleaning apparatus. One end of the plenum 42 is capped while the other end is coupled to a vacuum line, or both ends may be coupled to vacuum lines.
Areas of air restrictions in such vacuum systems typically result in large pressure drops, which greatly limit the air flow and therefore the capacity to effectively convey dust and contaminants to a collection point. Such systems also may have difficulties with dust and contaminants building up and plugging internal air passages in the equipment. The ability of the abrasive pad to clean and condition a moving surface is greatly reduced once contaminants build up on the pad's working surface because the build-up of contaminants on the abrasive pad working surface creates a barrier between the abrasive particles and the moving surface making the abrasive particle ineffective. Additionally, the moving surface, or roll surface, is often operated at a very high temperature (150° to 550° F.) and additional heat is generated by friction between the abrasive pad and the moving surface. As a consequence, the working lives of the abrasive pads are often too short due to exposure to process temperatures that exceed the capacity of the abrasive pad substrate material to withstand heat at such temperatures.
There is a need therefore, for a roll or web cleaning system that provides reduced build-up of debris during cleaning, and that provides improved operational life at high temperatures.